In the prior art, the high molecular weight linear polyesters and copolyesters of terephthalic and isophthalic acid are well known materials. They are described in the Whinfield et al Patent, U.S. Pat. No. 2,465,319 and Pengilly, U.S. Pat. No. 3,047,539 which are hereby incorporated by reference.
The linear polyesters have many properties such as a high heat distortion temperature, stiffness, solvent resistance and toughness which make them useful for many purposes. For many applications, it is desirable to upgrade the impact strength so that articles made of these polymers will not break when subjected to shock loading.
It has now been found that the addition of a thermoplastic poly(ester-urethane) to a linear polyester resin, will upgrade the impact strength without excessive loss of heat deflection temperature, tensile strength and flexural modulus. Also, it has been unexpectedly found that the thermoplastic poly(ester-urethanes) exhibit an excellent degree of compatibility when added to the thermoplastic linear polyesters. These blends show a degree of compatibility that occurs apparently on a molecular scale. The molded samples exhibit no evidence of separate phases such as delamination that occurs in incompatible polymer blends. Similar results have been noted in glass reinforced blends that have been prepared and tested.
It is, therefore, a primary object of this invention to provide novel linear polyester compositions that have improved impact strength.